The present invention relates to a nonaqueous electrolyte battery using a nonaqueous electrolyte for a battery reaction and a method for manufacturing it, and a positive active material and a method for producing it, and more particularly to a nonaqueous electrolyte battery and a method for manufacturing it in which preferable battery characteristics can be obtained, and a positive active material and a method for producing it.
Since lithium-ion secondary batteries have characteristics of light-weight and high energy density, they have been widely employed for mobile devices such as note book type personal computers, portable telephones, camcorders, etc. In the lithium-ion secondary batteries which are currently put to practical use, LiCoO2 of a layered rock salt structure is employed for a positive active material, however, cobalt is poor in resources and expensive, so that positive active materials are groped for in place of cobalt. Under the circumstances, LiNiO2 and LiMn2O4 have been known as materials functioning as positive active materials of the grade of 4 V and anticipated as active materials of a next generation.
However, since LiNiO2 is unstable in view of a crystal structure, its practical use has been delayed, and accordingly, LiNiO2 remains to be partly used only for certain kinds of devices. In the fields that will require large batteries of electric vehicles or the like in future, since it is anticipated that LiCoO2 and LiNiO2 are high in their cost and low in their reliability, there have been developed batteries using a spinel type lithium manganese oxide (LiMn2O4) low in its cost and high in its reliability.
However, since the crystal structure of the spinel type lithium manganese oxide is unstable in the above-described lithium-ion secondary battery, there is a possibility that a battery capacity is lowered when charging and discharging operations are repeated.
Further, when the lithium-ion secondary battery is stored at high temperature, manganese is eluted from a cathode using the spinel type lithium manganese oxide into electrolyte solution so that the eluted manganese is deposited on an anode. Thus, in the lithium-ion secondary battery, manganese deposited on the anode becomes a coat to prevent the doping and dedoping actions of lithium ions upon charging and discharging operations, which may possibly cause the battery capacity to be deteriorated.